The flaw relies on flaws in the Windows implementation of virtual 8086 (v86) mode to support DOS and 16-bit Windows apps in VDMs (Virtual DOS Machines). The problem can be fixed by users by removing support for 16-bit apps, for which Ormandy provides instructions. Note that 16-bit support is absent in 64-bit versions of Windows, and so is the flaw.

Such attacks were thought to be blocked by a series of mechanisms that Ormandy shows to be easily bypassed. Some are, arguably, flaws in Intel architecture, but in the main these are Windows design flaws.

Backward compatibility, even with ancient programs like DOS and Win16, but Microsoft still tries to maintain it. It may be time for such support, at the very least, to be turned off by default.

You can disable all 16-bit apps on your own system with the Local Group Policy Editor. While logged in as Administrator, run gpedit.msc. On the left, expand Local Computer PolicyComputer ConfigurationAdministrative TemplatesWindows ComponentsApplication Compatibility. On the right should be a policy named "Prevent access to 16-bit applications." Double-click it, select Enabled, and click OK. It appears that this policy creates a DWORD registry setting HKLM\System\CurrentControlSet\Control\WOW\DisallowedPolicyDefault and sets it to 1.

About the Author

Larry Seltzer has been writing software for and English about computers ever sincemuch to his own amazementhe graduated from the University of Pennsylvania in 1983.
He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find See Full Bio

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